[SPARK-24730] Add policy to choose max as global watermark when streaming query has multiple watermarks

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.3.1
• Fix Version/s: 2.4.0
• Component/s: Structured Streaming
• Target Version/s: 2.4.0
• Assignee: Tathagata Das
• Reporter: Tathagata Das
• Created: 03/Jul/18 04:27
• Updated: 13/Jul/18 05:25
• Resolved: 11/Jul/18 02:35

Description

Currently, when a streaming query has multiple watermark, the policy is to choose the min of them as the global watermark. This is safe to do as the global watermark moves with the slowest stream, and is therefore is safe as it does not unexpectedly drop some data as late, etc. While this is indeed the safe thing to do, in some cases, you may want the watermark to advance with the fastest stream, that is, take the max of multiple watermarks. This JIRA is to add that configuration.

Issue Links

• links to: [Github] Pull Request #21701 (tdas)